1. Field of the Invention Feline leukemia virus (FeLV) is a retrovirus having three subgroups designated A, B and C. FeLV is highly infectious among cats and is responsible for a number of diseases including lymphosarcomas, leukemias, thymic lymphomas, fibrosarcomas (with helper-dependent feline sarcoma virus), and non-regenerative anemias. FeLV infection in cats also causes suppression of the immune system which exposes the animal to opportunistic infection by a variety of pathogens.
A variety of vaccines against FeLV infection have been prepared, including attenuated live virus, killed virus, killed virus-infected cells, vaccines based on FeLV-tumor cell antigens, and vaccines based on viral envelope glycoproteins. None of these attempts have been wholly successful. The envelope glycoproteins utilized for vaccination were isolated from purified virus. Because of the difficulty in purification, only limited testing was performed and the dosages of the glycoproteins were low. The inoculated cats developed low levels of both precipitating antibodies and cytotoxic antibodies, and very low levels of neutralizing antibodies.
It would thus be desirable to provide a safe, reliable, and economic vaccine which provides effective protection against FeLV infection. It would be particularly desirable to provide relatively large quantities of FeLV envelope protein from a source other than the virus itself, which could additionally serve as a commercial supply for diagnostic assays.
2. Description of the Prior Art
Salerno et al., J. Natl. Cancer Inst. (1978) 6:1487-1493 have reported the use of an envelope glycoprotein isolated from purified FeLV as a vaccine. Hunsmann et al., Virology (1981) 113:602-612 have reported envelope glycoprotein acquire immunity to viral challenge. Lewis et al., Infection and Immunity (1981) 34:888-894, have described the use of a FeLV vaccine made of soluble tumor cell antigen. The use of glyceraldehyde-3-phosphate and pyruvate kinase promoters for gene expression in eukaryotic hosts is described in copending application Ser. No. 468,589, filed Feb. 22, 1983, in the names of Burke et al., the description of which is incorporated herein by reference.